Conventionally, in radio base stations, internal networks are formed by connecting multiple radio equipment control (REC) devices in a mesh manner. The REC devices (hereinafter, referred to as “relay devices”) mentioned here mean devices that control communication of the internal networks and perform a relay process on communication data.
The relay devices are connected to other relay devices using optical fibers that are called CPRI links that conform to interfaces of the CPRI standard that is the internal interface standard of the radio base stations. Each relay device continuously monitors whether transmission/reception between the relay devices is in a normal state, i.e., whether a CPRI link is established, and controls, in accordance with the monitoring result, disconnection/restoration of each CPRI link.
However, with the conventional relay devices, if any one of the CPRI links connected to its own relay device is disconnected, there may be a case in which another normal CPRI link (i.e., CPRI link is being established) is also recognized as being disconnected.
Accordingly, if conventional relay devices are used, there may be a case in which communication data cannot be relayed even though normal CPRI links still remain, which is a problem.
For example, a case will be described in which two relay devices (hereinafter, referred to as a “device B1” and a “device B2”) are connected, in parallel, on the higher-level device side (higher-level side) of a conventional relay device (hereinafter, referred to as a “device A”), and a single relay device (hereinafter, referred to as a “device C”) is connected on the lower-level device side (lower-level side) of the device A. In such a case, the device B1 and the device B2 on the higher-level side share the device C via the device A. The higher-level devices are, for example, radio base station control devices and the lower-level device is, for example, a mobile station device.
With the above-described device configuration, if the connection of a CPRI link from the higher-level side, i.e., between the device A and the device B1, to the lower-level side (hereinafter, referred to as a “downlink”) is disconnected, the device A detects that the disconnection has occurred in the downlink of the CPRI link from the device B1.
Subsequently, the device A performs a process for recognizing that a disconnection has occurred in the downlink of a CPRI link (normal link) from the device A to the device C. Therefore, the device B2 cannot communicate with the device C, with which the device B2 can in practice communicate.
Accordingly, there is a problem, if a CPRI link connected to its own relay device becomes abnormal, in how to implement a relay device that can maintain a data relay process using a normal CPRI link.
Patent Document 1: Japanese Laid-open Patent Publication No. 55-153045
Patent Document 2: Japanese Laid-open Patent Publication No. 62-245827